Control apparatus for vibration type actuator

ABSTRACT

The present invention relates to apparatus achieving improvement in operation characteristics in the operation of stopping or reversing the direction of or decelerating movement of a vibrating wave actuator constructed to apply an alternating voltage to an electro-mechanical energy conversion element to vibrate a vibration member to obtain a driving force. In the operation of stopping the vibrating wave actuator, it is necessary to cancel the vibration to stop the actuator, in order to stop the actuator in good response. The present invention has achieved the above object by applying an excitation signal, which excites vibration in a direction to cancel free vibration in the vibration member, to the electro-mechanical energy conversion element in the stop operation or the like.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to control apparatus for a vibration typeactuator.

In general, a vibration type actuator, such as a vibrating wave motor orthe like, has a vibration member in which driving vibration isgenerated, and a contact member in press contact with the vibrationmember; the driving vibration generated in the vibration member causesrelative movement between the vibration member and the contact member.

The vibration member typically is composed of an elastic member and apiezoelectric element, which functions as an electro-mechanical energyconversion element. For example, piezoelectric elements with drivingphases placed at positions with a spatial phase difference of 90°relative to the elastic member may be configured so that alternatingsignals of two phases with a phase difference of 90° may be applied tothe two driving phases so as to form respective bending vibrations onthe elastic member. In this manner a traveling wave is generated in thevibration member by composition of these bending vibrations, and thecontact body pressed against the vibration member is driven with adriving force by frictional contact therebetween.

A frictional material for obtaining the appropriate frictional force isbonded, applied, or formed on contact portions of the vibration memberand the contact member.

The elastic member forming the vibration member is made of a materialsuch as aluminum or the like, having a poor vibration damping property,i.e., a material resistant to damping of vibration.

In a vibration type actuator of this type, a variety of controloperations can be implemented by altering the phase difference betweenthe alternating signals of the two phases applied.

In the control apparatus for the vibration type actuator described inJapanese Patent Application Laid-Open No. 63-209478, the drivingvoltages applied in a stop operation are reversed in phase (forwarded orretarded by 180°) to hasten the stop operation. In the control apparatusfor the vibration type actuator described in Japanese Patent ApplicationLaid-Open No. 2-206373, voltages in a phase relation to reverse therotation in the stop operation are applied to hasten the stop operation.

SUMMARY OF THE INVENTION

An object of the invention associated with the present application is toprovide control apparatus for a vibration type actuator capable ofsecurely imparting sufficient vibration damping to the vibration memberin a stop operation or in a reversing operation.

In one aspect, the present invention is a control apparatus for avibration type actuator including a contact member is in press contactwith a vibration member having an electro-mechanical energy conversionelement, and in which a driving alternating signal is applied to theelectro-mechanical energy conversion element so as to generate a drivingvibration in the vibration member, thereby effecting relative movementbetween the vibration member and the contact member;

-   -   the control apparatus comprises a control circuit which applies        an excitation signal, which excites vibration in a direction so        as to cancel free vibration in the vibration member, to the        electro-mechanical energy conversion element during an operation        of decelerating or reversing or stopping a relative movement        between the vibration member and the contact member.

Other objects of the present invention will become clearer from thefollowing embodiments thereof described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the first embodiment;

FIG. 2 is a flowchart showing the operation of the first embodiment;

FIG. 3 is a graph showing the excitation phase and the level of residualamplitude in the case of weak exciting force;

FIG. 4 is a graph showing the excitation phase and the level of residualamplitude in the case of strong exciting force;

FIG. 5 is a block diagram showing the second embodiment;

FIG. 6 is a flowchart showing the operation of the second embodiment;

FIG. 7 is a graph showing the frequency characteristics of voltagesapplied to the vibration member and vibration of the vibration member;

FIG. 8 is a block diagram showing the third embodiment;

FIG. 9 is a flowchart showing the operation of the third embodiment;

FIG. 10 is an illustration showing the structure of the vibration typeactuator in the fourth embodiment;

FIG. 11 is a flowchart showing the operation of the fifth embodiment;

FIG. 12 is a timing chart illustrating changes of phases of pulsesignals;

FIG. 13 is an illustration showing the structure of the vibration typeactuator in the sixth embodiment;

FIG. 14 is a diagram showing a circuit configuration of power amplifyingmeans in the first embodiment; and

FIG. 15 is a timing chart showing waveforms in three-phase driving inthe first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below on thebasis of the drawings.

(First Embodiment)

FIG. 1 is a block diagram showing the first embodiment of the presentinvention.

In FIG. 1, numerals 1 and 2 designate piezoelectric elements which arebonded to an elastic member (not shown) which vibrates, for example, aring-shaped vibration member, when AC voltages (alternating signals) areapplied thereto. One piezoelectric element 1 and the other piezoelectricelement 2 are located, for example, with a positional phase differenceof λ/4, where λ is the wavelength at the resonance frequency. In each ofthe piezoelectric elements 1, 2, a plurality of regions with alternatelyvarying polarization directions are formed, for example, at intervals ofλ/2, and electrodes are formed in the respective regions. An electrodeis formed over the entire surface on the other side. Numeral 3 denotesvibration detecting means for detecting vibration generated in thevibration member; the vibration detecting means may be selected from apiezoelectric element, a strain gage, a magnetostriction element, anoptical sensor using a laser, and the like. Numeral 4 designatesposition detecting means for detecting the position of a moving member(not shown) which is moved by the vibration generated in the vibrationmember; numeral 5 designates power amplifying means which supplies theAC voltages with respective phase differences of 90° from each other, tothe piezoelectric elements 1, 2; numeral 6 designates an oscillator;numeral 7 designates driving signal generating means which divides anoutput signal from the oscillator 6 and outputs pulse signals of twophases; and numeral 8 designates phase shift means which shifts thephases of the two-phase pulse signals from the driving signal generatingmeans 7 in an identical phase direction by a phase shift amountaccording to a command from CPU 11 described hereinafter. An example ofthe power amplifying means 5 is presented in FIG. 14. Numeral 28designates a MOSFET driver which controls gate-terminal voltages ofMOSFETs of Q1 and Q2 according to a signal DA, which is a pulse signalsupplied from the phase shift means 8, and which normally amplifies thesignal DA with the amplitude of not more than 5 V to a pulse signal VAwith the amplitude of the power-supply voltage Vcc. The waveform of thesignal VA is dulled by inductance L and clipped at the power-supplyvoltage Vcc and at the GND potential by diodes D1, D2, whereby a signalPA comes to have a signal waveform of trapezoidal shape and is appliedto the piezoelectric element(s) PZT. The reason why the signal isclipped by the diodes in this way is as follows: in an ordinary system,without the diodes, energy stored in the inductor might obstructhigh-speed change of the phase of the signal PA, and for this reason,high-speed change of the phase of the signal PA is made feasible byflowing the energy of the inductor to the diodes in the present example.

Numeral 9 denotes position comparing means which compares the output ofthe position detecting means 4 with a position command from targetposition setting means (not shown); numeral 10 designates phasedifference detecting means which detects a phase difference between thephase of the driving voltage and the phase of the signal output from thevibration detecting means; and the CPU 11 issues a command of a phaseshift amount to the phase shift means 8 on the basis of the results ofthe output from the phase difference detecting means 10 and the positioncomparing means 9.

FIG. 2 is a flowchart showing the operation of the CPU 11.

At the first step the position comparing means 9 compares theinformation on the position of the moving member (current position) fromthe position detecting means 4 with the target position from theunrepresented command means (S1). When the result of the comparison isno agreement between them, the CPU sends a start command to theoscillator 6 and outputs a rotational direction command to the drivingsignal generating means 7 (S2).

Then the driving signal generating means 7 divides the output frequencyof the oscillator 6 to generate pulse signals of a predeterminedfrequency and two phases different 90° from each other. Since no phaseshift command is issued, the pulse signals are passed without any shiftthrough the phase shift means 8 and boosted by the power amplifyingmeans 5 to be applied to the piezoelectric elements 1, 2.

Then the vibration member excited by the piezoelectric elements 1, 2starts vibrating, whereby the moving member starts moving. The positiondetecting means 4 monitors the position of the moving member and theposition comparing means 9 compares the position of the moving memberwith the target position. This state is maintained until the position ofthe moving member comes to agree with the target position.

On that occasion, the phase difference detecting means 10 continuouslydetects and monitors the phase difference between the voltage applied tothe piezoelectric element 1 and the signal output from the vibrationdetecting means 3 detecting the vibration of the unrepresented vibrationmember (S3). When the position of the moving member comes to agree withthe target position (S4), operation of the CPU moves to S5.

When the position of the moving member agrees with the target position,the CPU calculates a phase shift amount so as to give a lag of 90° tothe phase of the voltage applied to the piezoelectric element 1,relative to the phase of the output signal of the vibration detectingmeans 3 on the basis of the result of the detection of the phasedifference at the phase difference detecting means 10, and outputs aphase shift command to the phase shift means 8 (S5).

It is configured that this state is maintained for a fixed period oftime (S6) and the CPU issues a command to stop oscillation to theoscillator 6 (S7).

The period before the stop of oscillation was the fixed period herein,but it may be a time proportional to a speed immediately before the stopoperation (or immediately before arrival at the target position),detected through the use of the position detecting means 4 or anunrepresented speed detecting means or the like, or a time correspondingto the speed.

The following will describe how the phase of the voltage relative to thephase of the vibration acts on damping of actual vibration.

The vibration displacement of the vibration member can be quickly dampedby supplying a force in a direction to cancel the velocity of the masspoint of the vibration member. When the motion of the mass point isrepresented by sin(ωt), the velocity of the mass point is given by thederivative thereof, cos(ωt). For decelerating the mass point by applyingan acceleration in the direction to reduce the velocity of the masspoint, it is necessary to supply a force with a phase shift of 180°relative to the phase of the velocity of the mass point.

Accordingly, the deceleration can be implemented by supplying the forcewith the phase represented by −cos(ωt). This force indicates a forcewith the phase lagging sin(ωt) by 90°.

In other words, the cancellation of vibration can be implemented bysuperimposing the vibration of the opposite phase over the vibration ofthe vibration member. In this case, since the vibration to cancel thevibration of the vibration member is of the phase lagging 180° behindthe phase of the vibration and since the free vibration lags the forceby 90° in phase, the force for generating the signal with the phase lagof 180° needs to have the phase leading the phase of the vibrationgenerated to cancel the vibration, by 90°; that is, the vibration can bedamped by applying a force with a phase lag of 90° behind the phase ofthe vibration of the vibration member.

Namely, the free vibration refers to a state of vibration without anyperiodical force acting on the vibration member. In this state thevibration member vibrates at the resonance frequency, which isdetermined by the shape of the vibration member, the pressed conditionthereof, and so on. If at this frequency an external force is exerted onthe vibration member the phase of motion of the vibration member lagsthe external force by 90°.

In order to cancel the vibration, a vibration with a phase lag of 180°behind the phase of the vibration of the vibration member issuperimposed on the vibration of the vibration member. Therefore, thevibration can be canceled when a signal with a lag of 90° behind thephase of the exciting force is equal to a signal with a lag of 180°behind the phase of the vibration of the vibration member. Thus, toapply an exciting force with a phase lead of 90° (because the vibrationlags the excitation by 90°) ahead a vibration generated for thecancellation operation (a vibration with a phase lag of 180° behind thevibration of the vibration member) is to apply an exciting force with aphase lead of 90° ahead of the vibration lagging the vibration of thevibration member by 180°. Namely, the vibration can be damped byapplying an exciting force with a phase lag of 90° behind the vibrationof the vibration member.

FIGS. 3 and 4 show the degree of damping of the vibration of thevibration member against the phase difference (which is negative whenthe excitation lags) between the phase of the vibration of the vibrationmember and the phase of the excitation applied in order to damp thevibration forcedly.

The negative domain indicates that the amplitude of the vibration isdamped, and 0 indicates no damping.

FIG. 3 shows a case of a weak exciting force for damping the vibration,in which the vibration is damped in the range where the lag of theexcitation phase is greater than 0° and smaller than 180°.

FIG. 4 shows a relation in the fastest damping case. It is seen that thedamping is largest when the phase of the exciting force lags the phaseof the vibration of the vibration member by 90°.

Since the damping is substantially determined by the phase as describedabove, the manner of damping can be arbitrarily controlled by changingthe phase.

FIG. 4 shows the fastest case of damping. The level of damping is −1 atthe delay of 90°, which indicates that the vibration is terminated bysingle excitation (excitation of a half period). In the case of FIG. 4,different from the characteristics of FIG. 3, it is shown that thevibration can be damped only within the range of 30° to 150°. In bothcases (FIGS. 3 and 4), the vibration exhibits the maximum increase atthe delay of 270° (i.e., at the lead of 90°).

It is seen from the above discussion that, for damping the vibration, itis necessary at least to supply the exciting force with the phase lag ofmore than 0° and less than 180° relative to the phase of the vibrationof the vibration member; otherwise the vibration is not damped, that,for excitation with a force to damp the vibration faster, it isnecessary to apply an exciting force with a phase lag of more than 30°and less than 150° relative to the phase of the vibration of thevibration member, and that, for damping the vibration fastest, it isnecessary to apply an exciting force with a phase lag of 90° relative tothe phase of the vibration of the vibration member.

In the operation of reversing the moving direction of the moving member,an acceleration operation is carried out using the applied voltages inthe phases in the reversing operation, instead of the stop operation inwhich the oscillator 6 was finally stopped in the present embodiment.

The present embodiment described a vibration type actuator operatingwith AC voltages of two phases, but it is clear that a like effect canbe achieved with the use of AC voltages of three or more phases. Thefollowing will briefly describe the vibration type actuator driven inthree phases. In the above-described example the vibration type actuatorwas one wherein two or more vibrations were generated at differentpositions or in different vibration modes by AC voltages of two phaseswith a phase difference of 90°, they were combined to create ellipticvibration at a contact portion with the moving member, and the ellipticvibration caused relative motion between the vibration member and themoving member. In contrast, in a three-phase driving operation, three ormore vibrations are generated at different positions or in differentvibration modes by AC voltages of three phases, for example, with aphase difference of 120° between them, to effect relative motion betweenthe vibration member and the moving member. FIG. 15 is a timing chartshowing the relationship between the vibrating state of standingvibration and applied voltage corresponding to each of the phases in theoperation of stopping vibration in a vibration type actuator in the caseof three-phase driving. A signal SA is an output signal from a vibrationdetecting sensor provided in the three-phase driving vibration typeactuator, and signals SB′ and SC′ represent vibration detection signalsexpected to be detected by vibration detecting sensors if they aregiven. Since a processing circuit will become complicated if thevibration detecting sensors are provided for the all three phases, onlyone phase is detected to set the phase of the applied voltage signal PAand the phases of signals PB and PC being applied voltages of the otherdriving phases are generated on the basis of the signal PA. It is shownthat by this method the standing vibrations corresponding to the phaseswithout the vibration detecting sensors are also damped similarly as thesignal SA is. The signals PA, PB, PC have waveforms of trapezoidal shapeand the phase difference between the signals is 120°. Before the timeA-A′, the phase difference is approximately 180° between the signal PA,PB, PC and the signal SA, SB′, SC′ indicating the vibrating state ineach phase of the vibration member in the vibration type actuator, whichindicates a state in which the vibration frequency of the vibrationmember is sufficiently higher than the resonance frequency of thevibration member and in which the velocity of relative motion betweenthe vibration member and the moving member in contact therewith issufficiently low. At the time A-A′, the stop operation of vibration isstarted. After the time A-A′, the signals PA, PB, PC are voltages withthe phase lead of about 90° relative to the phases of the appliedvoltages before the time A-A′. They have a phase lag of 90° relative tothe phases of the signals SA, SB′, SC′, indicating the vibrating statesin the respective phases of the vibration member in the vibration typeactuator. This results in quickly damping the amplitude of the vibrationin each phase. It is then detected at the time B-B′ that the amplitudeof the vibration becomes sufficiently small, and the applied voltagesPA, PB, PC thereafter are maintained in the state at the time B-B′. Inthe technology heretofore, it was common practice to employ the methodof bringing the applied voltages into 0 V or into an open state in thestop operation or the method of setting only the driver side of theinductor at 0 V, but the impact due to the final setting to 0 V wasexerted on PZT to cause excess vibration in certain cases. However, itbecomes feasible to stop the vibration quickly, by fixing the appliedvoltages last as shown in FIG. 15. The power supply may be considered tobe finally turned off in order to reduce power consumption, but thepower-supply voltage is normally not instantaneously converged to 0 Vupon interruption of power supply. Therefore, impact is little on thePZT, so as to cause no problem.

When the vibration of the vibration member is quickly switched fromprogressive vibration to standing vibration by the operation of quicklydamping the vibration in some phases in out of plural phases of ACvoltages, it is feasible to prevent production of big slip sound ordeterioration of the frictional surfaces even with occurrence of suddenhigh load.

It is assumed that the vibration detecting means used in the presentembodiment detects the independent standing waves generated by theexcitation from the respective piezoelectric elements 1, 2 individuallyor from only one of them. In the case where the resultant vibration ofthese standing waves is detected, the phase of the resultant vibrationis invariant if the exciting forces in the stop operation are applied soas to damp the respective standing waves at an equal damping speed.Therefore, the phases of vibration of the respective standing waves canbe readily detected from the phase of the resultant vibration, and thusit is not always necessary to detect the vibrations of the individualstanding waves.

Namely, positional phase shifts from the excited portions can be givenby preliminarily measuring the individual phases of the output signalsfrom the vibration detecting means 3 against the excitation voltages atthe resonance frequency, and thus the phases of the vibrations of thestanding waves can be calculated from the detection signal of theresultant vibration by subtracting the phases preliminarily measured andstored in a memory, from the detected phase. In the case where the ACvoltages applied to the piezoelectric elements 1, 2 are superimposed onthe detection signal from the vibration detecting means 3, it is clearthat the phases of standing waves are calculated by subtracting the ACvoltages from the detection signal or that the excitation phases in thestop operation can be determined in consideration of the phase shifts inthe superimposed case.

If the output of the vibration detecting means 3 is inverted or ispassed through a filter, the phase thereof will be shifted from theactual vibration phase. In these cases, it is clear that the phases ofthe AC voltages for the damping of vibration can be determined inconsideration of the phase shift due to this filter.

(Second Embodiment)

FIG. 5 is a block diagram showing the second embodiment.

In FIG. 5, numerals 12 and 13 designate inductor elements, such ascoils, transformers, or the like, intended to supply AC voltages to thepiezoelectric elements 1, 2 by dulling and boosting waveforms of ACvoltages of pulse shape output from the power amplifying means 5; andnumeral 14 designates amplitude comparing means which outputs the resultof comparison between the amplitude of the output signal from thevibration detecting means 3 and a comparison value from the CPU 11. Thevibration detecting means 3 stated herein may provide any value as longas it is a value corresponding to the amplitude of the vibration of thevibration member. For example, it can be an effective value, a meanvalue, a peak-to-peak value, a pulse width of a pulse signal obtained asa result of comparison of a vibration signal with a predetermined value,or the like.

FIG. 6 is a flowchart showing the operation of the CPU 11.

At the first step the position comparing means 9 compares theinformation on the position of the moving member from the positiondetecting means 4 with the target position from the unrepresentedcommand means (S11). When the current position does not agree with thetarget position, the CPU sends a start command to the oscillator 6 andoutputs a rotational direction command to the driving signal generatingmeans 7 (S12).

The driving signal generating means 7 divides the output frequency ofthe oscillator 6 to generate pulse signals of two phases with a phasedifference of 90° at a predetermined frequency. Since there is no phaseshift command issued, the pulse signals passing without any shiftthrough the phase shift means 8 are boosted by the power amplifyingmeans 5 to be applied to the piezoelectric elements 1, 2. Then thevibration member excited by the piezoelectric elements 1, 2 startsvibrating, whereby the moving member starts moving.

The position detecting means 4 monitors the position of the movingmember and the position comparing means 9 compares the current positionwith the target position (S13). Then the CPU waits until the movingmember arrives near the target position. When the current positionbecomes close to the target position, the driving frequency is set at afrequency for low speed drive (S14).

On that occasion, the driving frequency is normally set at apredetermined frequency higher than the resonance frequency or set so asto be gradually shifted to the higher frequency side and be swept up toa predetermined frequency.

Then this state is maintained until the position of the moving memberagrees with the target position. When the position of the moving memberreaches the target position (S15), the CPU sends a phase shift commandto advance the phase of the voltage applied to the piezoelectric element1 by 90°, to the phase shift means 8 (S16). In this state the amplitudecomparing means 14 compares the amplitude of the output signal from thevibration detecting means 3 with the comparison value from the CPU 11(S17). After the amplitude is detected becoming smaller than thecomparison value, i.e., after the vibration of the vibration member isjudged as sufficiently damped, the CPU sends a command to stop theoscillation, to the oscillator 6 (S18).

In the first embodiment the phase was set so as to lag the vibration ofthe piezoelectric element 1, whereas in the present embodiment the phaseof the AC voltage is given a lead of 90°, the reason for which will bedescribed below.

FIG. 7 is a Bode diagram showing the frequency characteristics of thedriving voltage and actual vibration. Solid lines represent thecharacteristics of the voltages applied to the piezoelectric elementsagainst the output voltage of the power amplifying means 5, and dashedlines the characteristics of the vibration of the piezoelectric elementsagainst the driving voltage.

The voltages applied to the piezoelectric elements 1, 2, indicated bythe solid lines, have a phase lag at the resonance frequency (near 36kHz) of the vibration member because of the influence of the inductorelements 12, 13, but there is almost no lag near 40 kHz, above theresonance frequency.

As is apparent from the characteristics of the amplitude of thevibration of the piezoelectric elements indicated by the dashed line,the amplitude of the vibration is large around the resonance frequencyof the vibration member, and decreases as the frequency increases ordecreases.

Accordingly, in order to move the position of the moving member quicklyto the target position, it is necessary that the frequency of the ACvoltages applied to the piezoelectric elements 1, 2 be set as close tothe resonance frequency as possible to move the moving member at highspeeds and that, in order to stop the moving member at the targetposition with high accuracy, the frequency of the AC voltages be setapart from the resonance frequency to stop the vibration after dampedsufficiently.

In the case of the present embodiment, since the frequency of the ACvoltages is set on the higher side, higher than the resonance frequency,the vibration characteristics of the piezoelectric elements 1, 2 have aphase lag of 90° behind the applied voltages at the resonance frequency,but the phase difference is approximately 180° near the target position,because the frequency near the target position is set higher than theresonance frequency in order to get ready for the stop operation.

Accordingly, in the first embodiment, the optimal phase of the excitingforce for the stop operation of vibration was a phase with a phase lagof 90° behind the phase of the vibration. When this is applied to thepresent embodiment, since the vibration of the vibration member lags180° behind the applied voltages near the target position, it becomesfeasible to implement a quick stop operation by applying an excitingforce with a phase lag of 270° further lagging the vibration by 90°,i.e., by exerting an exciting force with a phase lead of 90° relative tothe applied voltages.

In the present embodiment the oscillator 6 was stopped when theamplitude of the variation of the vibration member became smaller thanthe predetermined amplitude, but the oscillator 6 may also be stoppedwhen change in the output from the position detecting means 4 comes tofall within a predetermined range.

The present embodiment used the position detecting means 4, but it isalso possible to employ a configuration wherein there is provided avelocity detecting means for detecting the velocity of the moving memberand the oscillator 6 is stopped when the velocity of the moving memberbecomes smaller than a predetermined value.

For reversing the moving direction of the moving member, it can beimplemented by performing an acceleration operation using the phases ofthe applied voltages for the reversing operation, instead of the stopoperation of the oscillator 6 carried out in the above embodiment.

The following problem can be circumvented by carrying out the vibrationdamping operation after achievement of sufficient deceleration as in thepresent embodiment described above. It is a phenomenon becoming serious,particularly, in the case of the quick stop operation, which is residualvibration after the relative motion between the moving member and thevibration member is stopped to unite the moving member and the vibrationmember. It is vibration at the natural frequency determined by therigidity of an unrepresented support member supporting the moving memberor the vibration member and the weight of the moving member and thevibration member, and the remaining time of this vibration becomeslonger as the impact upon the stop operation increases.

Namely, supposing that the vibration member is supported on a stationarymember by springs, when the moving member is quickly stopped from amoving state at a high speed, a relative force acts between thevibration member and the moving member, so that the springs supportingthe vibration member are displaced to induce vibration due to the totalmass of the vibration member and the moving member, and the springs.Since the relative force occurring between the moving member and thevibration member is smaller in the quick vibration damping operationafter sufficient damping of the vibration of the vibration member thanin the damping operation on the way of the high-speed operation, theremaining time of vibration becomes shorter.

In the present embodiment the moving velocity was decreased by settingthe driving frequency at a frequency higher than the resonancefrequency, but the moving velocity can also be decreased by setting thedriving frequency conversely at a frequency lower than the resonancefrequency. In this case, since the phase of the vibration of thevibration member becomes closer to the phase of the applied voltages,the way of shifting the phase in the stop operation is different fromthat in the case of a frequency higher than the resonance frequency. Inthis case, since the phase of the vibration of the vibration memberbecomes close to 0° relative to the phase of the applied voltages, thephase of the applied voltages is given a lag of 90° relative to thephase of the applied voltages immediately before the start of the stopoperation.

(Third Embodiment)

FIG. 8 is a block diagram showing the third embodiment of the presentinvention.

In FIG. 8, numeral 15 designates power amplifying means which amplifiespulse signals of four phases output by making use of a timer function ofthe CPU 11, and numerals 16 and 17 designate transformers, to theprimary side of each of which the opposite phases out of the four-phaseoutput voltages from the power amplifying means 15 are connected. HighAC voltages of two phases are generated on the secondary side of thetransformers to be applied to the piezoelectric elements 1, 2.

The frequency of the AC voltages is set by a frequency dividing ratewhich is set in a programmable frequency divider in the CPU 11 to dividea pulse signal of several ten MHz from the oscillator 6 with enhancedstability, for example, through the use of a quartz oscillator, and thepulse width of the output signal from the CPU 11 is set by counting thetime corresponding to the pulse width by a timer. In the firstembodiment described above the oscillator 6 was stopped to stop thedriving voltages, whereas in the present embodiment the oscillator 6always oscillates after supply of power, and in the stop operation thepulses of four phases output from the CPU 11 are kept all at the samelevel.

By keeping the pulses of four phases all at the same level, it isassumed that drivers are connected in the push-pull configuration to theprimary side of the transformers, and it is meant that the voltagesbetween the two terminals on the primary side are set equal in the stopoperation.

The amplitude of the voltages applied to the piezoelectric elements 1, 2can be changed by changing the pulse width, whereby the exciting forcein the stop operation can be set at an arbitrary value. In the secondembodiment described above the amplitude comparing means 14 and theposition comparing means 9 performed the comparison operations ofamplitude and position, whereas in the present embodiment such data isread into the CPU 11 and the comparisons are made by software.

FIG. 9 is a flowchart showing the operation of the CPU 11.

At the first step the information on the position of the moving memberfrom the position detecting means 4 is compared with the target positionfrom the unrepresented command means (S31). When the current position isnot equal to the target position, the CPU determines the frequency, thepulse width, and the phase difference and outputs the pulse signals offour phases (S32). This phase difference is a value determined accordingto the moving direction. The four-phase pulse signals are pulse signalswith phase intervals of 90°, and the four-phase pulse signals areboosted by the power amplifying means 15 to be applied to thepiezoelectric elements 1, 2.

Then the vibration member excited by the piezoelectric elements 1, 2starts vibrating, whereby the moving member starts moving. The positionof the moving member is monitored by the position detecting means 4 andis compared with the target position (S33). Then the CPU waits until themoving member arrives near the target position. When the moving memberarrives near the target position, the driving frequency is set to afrequency for low speed drive (S34).

On that occasion, the driving frequency is normally set at apredetermined frequency higher than the resonance frequency or set so asto be gradually shifted to the high frequency side and swept up to apredetermined frequency.

Then this state is maintained until the position of the moving memberagrees with the target position (S35). When the position of the movingmember reaches the target position, the internal timer in the CPU 11 isset so as to advance the phase of the voltage applied to thepiezoelectric element 1 by 90° (S36). The AC voltages with a phase leadof 90° are applied until the amplitude detected by the vibrationdetecting means 3 becomes smaller than the predetermined amplitude. Whenthe amplitude reaches the predetermined amplitude (S37), the outputs ofthe four-phase pulse signals are fixed at the same level (S38), wherebythe voltages applied to the piezoelectric elements 1, 2 are set to 0.

The amplitude of the AC voltages with a phase lead of 90° is configuredto be set according to the amplitude of the vibration of the vibrationmember being the output from the vibration detecting means 3, which canbe implemented by changing the pulse width of the four-phase pulsesignals output from the CPU 11.

Concerning in what relation the pulse width is set with the amplitude ofthe vibration of the vibration member, the pulse width can be set, forexample, as a value proportional to the amplitude of the vibration or aresult of addition of a predetermined value to the value proportional tothe amplitude of the vibration.

The pulse width of the four-phase pulse signals may also be set in sucha way that a target damping curve is first set for the amplitude of thevibration, the actual amplitude of vibration is compared with the curve,and the pulse width is determined based on the result of the comparison(e.g., based on a value of integration of the comparison result).

How to change the pulse width can be a method of changing the pulsewidth on the basis of a predetermined pattern according to the amplitudeof the vibration of the vibration member immediately before the start ofthe stop operation or according to the velocity immediately before thestart of the stop operation of the moving member moved by the vibrationof the vibration member. For example, the greater the amplitude of thevibration or the higher the velocity, the longer the time for the stopoperation of the vibration of the vibration member. Therefore, it isnecessary to set an amount of change of the pulse width per unit time.

In the present embodiment the damping speed of the vibration of thevibration member was changed by changing the amplitude of the ACvoltages applied to the piezoelectric elements 1, 2, because theamplitude of the voltages was proportional to the exciting force. It isalso possible to change the damping speed of the vibration of thevibration member similarly by changing the phases of the exciting ACvoltages relative to the phase of the vibration of the vibration member,as shown in FIGS. 3 and 4.

In the case of the phase difference, the phase for maximum damping is90°, and any desired damping can be achieved by shifting the phase from90°.

Accordingly, the damping speed of vibration can also be controlledsimilarly by changing the phases of the four-phase pulse signals insteadof the pulse width in the present embodiment.

The above described the stop operation, and the following will describethe operation of reversing the moving direction of the moving member.

In the reversing operation, the four-phase pulse signals are outputaccording to a procedure similar to that in the above description, thefour-phase pulse signals are set so as to be in a phase relation toreverse the moving direction, instead of fixing the outputs of thefour-phase pulse signals, and the frequency and pulse width are changedaccording to a predetermined operation to accelerate the moving speed.

In the present embodiment the pulse width was changed to change theamplitude of the applied voltages, but the same can be implemented bychanging the power-supply voltage, the amplification rate, etc. of thepower amplifying means 5.

In the present embodiment the amplitude of the voltages was changed tochange the exciting force, but a like effect can also be attained by aconfiguration wherein the exciting force is intermittently applied andtime intervals and excitation durations for application of the excitingforce are used as parameters, whereby a time-averaged value of theexciting force can be changed based on the parameters even at the sameapplied voltages.

(Fourth Embodiment)

FIG. 10 is an illustration showing the structure of the vibration typeactuator used in the fourth embodiment of the present invention.

In FIG. 10, numerals 18 and 19 designate piezoelectric elements, andnumerals 20 and 21 designate vibration members. AC voltages from ACvoltage supply means (not shown) are applied to the piezoelectricelements 18 and 19 to excite vibration in the vibration members 20, 21.Numerals 22 and 23 denote moving members kept in press contact with thevibration members 20, 21 by pressing members (not shown), and 24designates a rotational shaft which is coupled to the moving members 22,23.

When the rotational shaft is coupled to the moving members driven by aplurality of vibration members in this way, if the vibration membersprovide respective outputs of different tendencies to the rotationalshaft 24, there will arise a problem of degrading the total efficiency.

Since the two moving members 22, 23 are coupled by the rotational shaft24, if there remains vibration of the vibration member 21 even after astop of the vibration of the vibration member 20, an extra time will betaken for the stop of the moving members 22, 23 and the moving member 22will slip on the vibration member 20 to raise a problem of deterioratingthe frictional surfaces.

In order to make both vibration members 20, 21 draw the same vibrationdamping curve in the stop operation of the vibration members 20, 21, thephase and amplitude of the AC voltages are changed in a predeterminedpattern on the piezoelectric elements 18, 19 and thereafter the supplyof the AC voltages is stopped, thereby stopping the vibration quicklyand preventing deterioration of the frictional surfaces.

(Fifth Embodiment)

FIG. 11 is a flowchart showing the operation of the CPU 11 in the fifthembodiment of the present invention. The block configuration in thepresent embodiment is the same as in FIG. 8 and illustration thereof isthus omitted herein.

In the present embodiment, in the stop operation an overrun amount at astop operation is calculated from the amplitude of the vibrationimmediately before a start of the stop operation and the stop operationis started from the overrun amount before the target position.

At the first step the information on the position of the moving memberfrom the position detecting means 4 is compared with the target positionfrom unrepresented command means (S41). When the current position of themoving member does not agree with the target position, the CPUdetermines the frequency, the pulse width, and the phase difference andoutputs the pulse signals of four phases (S42).

The four-phase pulse signals are boosted by the power amplifying means15 to be applied to the piezoelectric elements 1, 2. Then theunrepresented vibration member excited by the piezoelectric elements 1,2 starts vibrating, whereby the moving member starts moving. Theposition detecting means 4 monitors the position of the moving memberand the current position of the moving member is compared with thetarget position (S43). Then the CPU waits until the moving memberarrives near the target position. When the moving member arrives nearthe target position, the CPU sets the driving frequency to a frequencyfor low speed drive. On that occasion, the driving frequency is normallyset at a predetermined frequency higher than the resonance frequency orset so as to be gradually shifted to the high frequency side and beswept up to a predetermined frequency.

Then the CPU monitors the output from the vibration detecting means 3and estimates the overrun amount at the stop operation according to astop sequence of changing the phase and amplitude of the AC voltages.

Then the CPU sets a new target position at a position the estimatedoverrun amount before the old target position (S44), and this statecontinues before the position of the moving member agrees with the newtarget position (S45). This operation of estimating the overrun amountis continuously carried out up to the start of the stop operation.

When the position of the moving member reaches the new target position,the internal timer in the CPU 11 is set so as to advance the phase ofthe voltage applied to the piezoelectric element 1 by 90° (S46). Thenthe AC voltages with a phase lead of 90° are applied until the amplitudedetected by the vibration detecting means 3 becomes smaller than thepredetermined amplitude (S47). When the amplitude reaches thepredetermined amplitude, the outputs of the four-phase pulse signals arefixed at the same level (S48) to set the voltages applied to thepiezoelectric elements 1, 2 to 0.

FIG. 12 shows an operation of advancing the phase of a pulse signal by90°. The signal C indicates the original waveform (the waveform innormal driving).

If the actual position becomes equal to the foregoing new targetposition at a point before the point A-A′ the signal is changed to thesignal D.

However, since it is impossible to advance the phase by 90° like thesignal D after the point A-A′ the pulse edge is shifted to the nextphase change point B-B′ after the point A-A′ so that the signal becomeslike the signal E.

In the case where the actual position becomes equal to the new targetposition around the point A-A′ the vibration damping effect will appeareven with a slight shift from 90° like the signals F and G if it isclose to the point A-A′.

Concerning the estimation of the overrun amount, since the overrunamount is approximately proportional to the square of the movingvelocity immediately before the start of the stop, the overrun amountcan be readily calculated from the moving velocity if a coefficient ofthe proportional relation is preliminarily determined.

(Sixth Embodiment)

FIG. 13 is an illustration showing a configuration example of thevibration type actuator of the standing wave type rotated by an ACvoltage of one phase in the sixth embodiment of the present invention.

In FIG. 13, numeral 25 designates a stacked piezoelectric element,numeral 26 designates an elastic body comprised of an elastic member,and numeral 27 designates a moving member. When an AC voltage is appliedto the piezoelectric element 25, the elastic member 26 vibratesvertically, whereby the moving member 27, which is pressed byunrepresented pressing means against a projection 26 a mounted obliquelyrelative to the direction of the rotor shaft on the elastic member 26,starts rotating in one direction.

In the vibration type actuator rotated by an AC voltage of one phase, asdescribed above, it is clear that quick damping control on the amplitudeof the vibration of the vibration member can be attained by controllingthe phase of the AC voltage applied to the piezoelectric element 25.

The vibration type actuator of the configuration of the presentembodiment can also be constructed, for example, as in the embodimentshown in FIG. 10, so as to be applied to the structure for driving acommon load by a plurality of rotors.

1. A control apparatus for a vibration type actuator including a contactmember in press contact with a vibration member having anelectro-mechanical energy conversion element in which a drivingalternating signal is applied to the electro-mechanical energyconversion element to generate driving vibration in the vibrationmember, thereby effecting relative movement between the vibration memberand the contact member, said control apparatus comprising: a detectingcircuit that detects a vibration of the vibration member and outputs acorresponding signal; and a control circuit that detects a vibration ofthe vibration member and outputs a corresponding signal; and a controlcircuit that applies an excitation signal to the electro-mechanicalenergy conversion element in an operation of decelerating or reversingor stopping a relative movement between the vibration member and thecontact member, the excitation signal being controlled so as to excitethe vibration in the vibration member in a direction that cancels freevibration in the vibration member, according to the signal output fromthe detecting circuit, wherein in an operation of reversing a movingdirection of the relative movement between the vibration member and thecontact member, the moving direction is reversed after application ofthe excitation signal for a period of a predetermined time or a timedetermined according to a velocity or amplitude of the vibrationimmediately before a start of a stop operation.